In wireless packet-data networks with centralised control, a mechanism is required to enable a base station (or eNB in UMTS LTE terminology) to deliver both common and dedicated system control information to a number of mobile stations. Information of common interest to all such mobile stations may include system configuration, access information and so on. Information of dedicated interest to a particular mobile station (or mobile station group) may include indication of incoming user data, assignment of uplink resources and so on. Mobile stations are expected to monitor for messages containing such information and, when necessary, respond in a timely and appropriate manner.
In comparison to the majority of user data carried by such networks, system control messages of the type described constitutes a relatively low rate data stream, much of which is event-driven. Furthermore, the majority of dedicated system control information will be irrelevant to the majority of mobile stations. The monitoring of this information, particularly while a mobile station is in an inactive mode, consumes energy for, often, no benefit. For battery-operated mobile stations, this is of crucial importance because energy consumed by this monitoring process has a great impact on the station's autonomy. Accordingly, such networks make provision for mobile stations to monitor only a fraction of system control messages transmitted by a fixed station, ensuring, nevertheless, that the mobile station receives all information that is relevant to it. This implies a reception schedule observed by the mobile station and known to the fixed station. In a further means of reduction of energy consumption, the fixed station may transmit a plurality of pointers to updated common or new dedicated information; the mobile station, on receiving such a pointer can arrange to receive further transmissions as indicated or simply go back to sleep if none of the said plurality of pointers is relevant.
In some systems, for example, LTE Rel. 8, the reception schedule is imposed by the fixed station. In the case of LTE, under a feature known as Discontinuous Reception (DRX), the fixed station may individually instruct each mobile station that is (wirelessly) connected to it to observe a reduced reception schedule, allowing it to miss a certain proportion of possible instances of scheduled transmissions. In principle, DRX parameters can be set to provide the best balance between responsiveness to incoming signals and messages on the one hand and battery life on the other.
In LTE, this process is handled by the Radio Resource Control entity at layer 3, which does not necessarily take into consideration the capabilities and current statuses of each mobile station thus addressed—nor, in fact, is it obliged to. As the spread of applications and range of physical embodiments of mobile stations both grow in response to the further flexibility of next generation standards, the centralised approach of release 8 becomes ever more a compromise. To take one example, mobile stations have increasingly sophisticated battery management systems and yet are unable to signal to the fixed station their current battery status. Such a station is obliged to conform to a preset cycle even if it becomes aware that its battery is perilously close to empty. Conversely, when placed on a charger, the same station is unable to signal that it is ready to adopt a faster wake-up cycle and thereby increase its responsiveness to incoming messages. In the case of embodiments in the form of computer data cards that can draw their power from the host computer, they may be sensitive to the host's own power management mechanisms and the communications requirements of applications running on the host.
What is needed is a means of allowing the mobile station to update the fixed station of its status in a dynamic manner.
In practice, the fixed station also has to balance its resources across the whole plurality of mobile stations connected to it. It therefore needs to retain overall control over the scheduling of system control information. Nevertheless, the possible rise of so-called femto cells could mean the existence of a whole class of LTE-based fixed stations each serving a relatively small number of mobile stations.